The machine described in the prior art statement has met with considerable financial success. However, the machine exhibits certain undesirable characteristics which limit its potential usefulness in some newly proposed applications.
For example, the timers employed utilize synchronous motors whereby slight normal frequency variations in the alternating current feed can cause undesired variations in the time of generation of control signals and some of the folds can be formed unevenly. This is particularly disadvantageous when the folded curtains are to be placed in transparent packages since curtains with uneven folds are visually unattractive.
In addition, the time delay networks employ discrete components having values which may change somewhat as the components age and in addition these values are somewhat temperature dependent. These changes in values change the time constant and since the duration of each jet of air is determined by the associated time constant, the actual duration may increase or decrease as compared to the nominal duration desired. Such increases or decreases also adversely effect the folding operation because over or under folding can occur.
Moreover, as has been previously explained, the input roller stops rotating and at the same time the third folding operation is initiated. However, this action limits the length of the curtain that can be folded because unless the curtain is sufficiently short for its trailing edge to have cleared the input section at the time the third fold operates, the trailing edge will be trapped in the input section when the input roller stops rotating and the machine will become jammed.
The present invention is directed toward an improved machine of the type described above wherein the timing of the folding operations and the duration of the various air jets is controlled to a very high degree of precision whereby the folds can be formed evenly without appreciable over and under folding and moreover wherein the lengths of curtains to be folded can be substantially increased without jamming the machine.